In the context of gas turbine engines, maintenance of highly pressurized air is essential for the functionality of the engine. If air is allowed to leak across these seals, this may significantly diminish the functionality of engine itself. For example, air leakage can lead to increase fuel consumption, reduce engine efficiency, and increase maintenance costs by increasing turbine inlet temperatures. Additionally, leakage of liquids into a high pressure compartment of a turbine engine also affects performance of the equipment where the seal is used. Specifically, lubricant leakage during static or dynamic situations can lead to oil coking, engine fire or the production of noxious odor therefrom. Accordingly, in many gas turbine applications it is important that seals maintain each fluid in its respective compartment without allowing uncontrolled leakage.
Typically, labyrinth seals are employed at specified sealing locations to control leakage of high pressure gas, e.g. gas discharged from a compressor, from a high pressure area to a low pressure area. Labyrinth seals operate by throttling gas flow through a series of annular constrictions formed between annular teeth, which may be located on a rotating component, and an annular rub strip, which may be located on a stationary engine member. The rub strips are abradable to allow the teeth to rub lightly during dynamic operating conditions, such as thermal transients or maneuvering loads. The effectiveness of these labyrinth seals is dependent on keeping the radial clearance between the rub strip and teeth to a minimum. However, the minimum radial clearance is limited by manufacturing tolerances, rotor concentricity control, and thermal growth between rotating and stationary components. If the radial clearance is too small, this results in premature seal wear and possible engine damage. Conversely, if the radial clearance is too large, this results in excess leakage.
U.S. Pat. No. 3,383,033 discloses a gas bearing face seal as an alternative to the labyrinth seal. In the gas bearing face seal, an air bearing is used to actively control the spacing between a flow restricting tooth and a rotating sealing surface on a rotating component. A face seal ring member, which carries the restricting tooth, is supported for movement toward the rotating sealing surface. A ring seal, such as a piston ring seal, provides a secondary seal between the ring member and a stationary engine frame. During low or no power conditions the ring member and restricting tooth are biased away from the rotating sealing surface by springs. During higher power operation high pressure compressor discharge air acts on the ring to urge the ring and tooth toward the sealing surface. A portion of the high pressure discharge air is supplied to a gas bearing space between the ring and the rotating sealing surface to establish a predetermined gas bearing face clearance. Pressure forces developed in the gas bearing space oppose further motion of the ring and tooth toward the sealing surface, and permit close spacing of the restricting tooth with respect to the sealing surface by actively maintaining the predetermined clearance. Further motion of the ring and tooth toward the rotating sealing surface increases the pressure force in the air bearing space, thereby urging the ring and tooth away from the sealing surface to maintain the predetermined clearance.
While the seal as disclosed in U.S. Pat. No. 3,383,033 attempts to overcome disadvantages of the labyrinth seal, the disclosed seal itself includes a number of significant disadvantages. First, the disclosed seal does not include a means for maintaining the ring member concentric with respect to the axis of the engine or with other seal components. To this end, the seal is imbalanced and does not create an effective seal. Second, the seal as disclosed shows the ring member pressurized radially inwardly by the higher pressure region. Rings pressurized radially inwardly will deform to an out-of-round shape with reduced sealing capability unless they are sufficiently massive and stiff. Third, differential thermal growth and other effects influencing the clearance between the seal housing and face seal ring member can result in changes in pressure forces acting on seal components, which can result in poor sealing. Fourth, the seal as disclosed includes an auxiliary restrictor tooth integral with or mounted on the ring member, which adds weight to the ring member, and increases pressure closing forces on the ring member, with the result that heavy spring means must be used to bias the ring member away from the sealing surface. Finally, the seal does not efficiently vent air exiting the air bearing space and the restrictor tooth to the low pressure region.
Another alternative to the labyrinth seal is set forth in U.S. Pat. No. 5,284,347. More specifically, U.S. Pat. No. 5,284,347 describes an aspirating seal operation within a turbine engine. The face seal is normally retracted away from the rotor face during startup and shutdown conductions in the engine when there is an insufficient change in pressure between the high pressure and low pressure compartments. As pressure builds in the engine, the seal starts to close towards the rotor due to a thrust balance that develops across the area defined by the seal aspirator tooth and seal dam. The seal continues to move closer towards the rotor until the operating gas film is established by the high pressure air entering the hydrostatic gas bearing orifices. The seal reaches equilibrium when the force balance is satisfied, i.e. the opening forces equal the closing forces. However, in a static state there is no seal between the high pressure compartment and low pressure compartment. Accordingly, there is no seal to prevent any lubricant, such as oil, that may be contained within the low pressure compartment from leaking into the high pressure compartment. Leakage of liquids into the high pressure compartment adversely affects performance of the equipment where the seal is used. In case of an aircraft engines, oil leakage across the seal into a hot air side may cause oil coking or an engine fire. When an oil lubricant is used, mixing the oil with the gas could result in formation of oil coke, a byproduct of oil heated to an elevated temperature, which chemically alters the oil and is detrimental to the gas turbine. Oil coke can foul seal surfaces reducing the integrity of the seal and prevent proper bearing lubrication within the lubricant sump. Finally, oil coking often leads to a noxious odor that may flow into a passenger space of the vehicle. This odor can be unpleasant and alarming to passengers unaware of the source of the smell.
Based on the foregoing, a seal for a turbomachine is desirable that maintains the seal member in a balanced state with respect to the axis of the engine or with other seal components in both a static and dynamic condition. Moreover, a seal for a turbomachine is desirable that is adapted to separate a high pressure compartment from a low pressure compartment during a dynamic state by an operating gas film created by the seal. Furthermore, a seal for a turbomachine is desirable that is adapted to prevent lubricant movement between a low pressure compartment and a high pressure compartment in either a static and a dynamic state.
The present invention addresses, at least, the forgoing needs.